This invention relates to a novel method for preparing a screen structure for a CRT (cathode-ray tube) and particularly, but not exclusively, to a novel method for preparing a light-absorbing matrix for a color-television-picture tube.
Some color-television-picture tubes include, as a structural part of the luminescent viewing screen, a light-absorbing matrix located on the inner surface of the faceplate of the tube. The matrix has a multiplicity of openings therein, which may be in the shape of dots or lines, with phosphor filling each opening in the matrix. A reverse-printing method for preparing a light-absorbing matrix for a CRT is described in U.S. Pat. No. 3,558,310 issued Jan. 26, 1971 to E. E. Mayaud. In a preferred embodiment of that method, the inner surface of the faceplate of a CRT is coated with a film of clear water-based photosensitive material, typically a dichromate-sensitized polyvinyl alcohol. A light image is projected on the film to insolubilize selected regions of the film. The film is flushed with water to remove the still-soluble regions of the film while retaining the insolubilized regions in place. Then, the developed film is overcoated with a layer containing particles of screen structure material, such as graphite. Finally, the retained film regions are removed together with the overlying overcoating, while retaining those portions of the overcoating in the regions previously occupied by removed still-soluble portions of the film. Such a process produces satisfactory screen structures, although further improvements in the process are desirable, for example, by providing shorter exposure times for the film and better definition of the structure.
Further improvements towards this end are disclosed in U.S. Pat. No. 4,049,452 issued Sept. 20, 1977 to E. M. Nekut. The method disclosed in the Nekut patent is similar to the method disclosed in the Mayaud patent except that the film contains 5 to 80 weight percent of at least one diol from a specified group.